C1-C2 fusion

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  1. Anterior or posterior translation of C1 normally occurs; there is 40 degrees of axial rotation and 20 degrees of combined flexion and extension and 5 degrees of lateral bending at C1 and 2
  2. Instability appears as subluxation or spinal deformity accompanied by severe pain or neurological deficits
  3. Steele’s rule of thirds: at the craniovertebral junction, the spinal canal at the C1 level is occupied equally by three components: the odontoid process, the spinal cord, and the subarachnoid space; thus even minor trauma can cause permanent paralysis or sudden death
  4. Occipitoatlantal instability is demonstrated by movement between the dens and basion or vertical migration
    1. normal atlas is relatively fixed to the occipital condyles and skull base
    2. C1 acts like a washer entrapped between the skull and C2
    3. transverse and and alar ligaments are strong and allow rotation around the dens
    4. symptoms of occipitoatlantal instability
      1. most have symptoms of myelopathy
      2. downbeat nystagmus
    5. reasons to fuse O-C2
      1. widespread bone destruction
      2. absence of C1 arch
      3. upward migration of odontoid into foramen magnum
      4. irreducible shifts of C1 or C2
      5. burst fractures of C1 (but probably treated well with immobilization)
    6. down side of occipital-cervical fusion: lose 30% of flexion/extension (13 degrees at O-C1 junction), lose at least 40 degrees of lateral rotation and 8 degrees of lateral bending
  5. Atlantoaxial stabilization
    1. anterior approaches
      1. anterior C1-C2 facet screw fixation
      2. odontoid screw fixation
    2. posterior approaches
      1. C1-C2 wiring and bone graft
        1. Interspinous fusion – notches in C2 spinous process to seat wire, bicortical strut graft, wire posterior to arch of C1; strut graft trapped anterior and posterior
        2. Brooks fusion - wires are halved and passed sublaminar beneath C1 and C2, bilateral wedges of bone; Remember: Brooks is Bilateral
        3. Gallie fusion – loop of wire secured beneath C2 spinous process, unicortical graft is notched to fit over the spinous process of C2
      2. Posterior C1-C2 facet screws
        1. Entry point around T1 or T2, screws through pedicle of C2, across the C1-C2 facet and into the C1 lateral mass
      3. C1-C2 Halifax clamps
        1. Compression clamps with bicortical bone graft in between C1 and C2
  6. Occipitocervical stabilization
    1. wire and bone grafts
      1. two holes in occiput, sublaminar wires or holes in spinous process
      2. may make holes in the facets after remove the articular cartilage if a laminectomy has been performed
    2. Steinmann pin, metal rods
    3. Occipitocervical screw plate
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